ADDITION-ELIMINATION REACTION IN THE TRIFLUOROACETYLATION OF ELECTRON-RICH OLEFINS

Reactions of electron-rich olefins such as vinyl ether 1 and vinyl sul fide 2 with trifluoroacetic anhydride in carbon tetrachloride at room temperature proceeded by the formation of addition products 7 and 8, r espectively, which were identified as stable intermediates by H-1 NMR and IR spectra, eventually giving the, corresponding trifluoroacetylat ed olefins 5 and 6 as substitution products. These reactions were also observed in chloroform and dichloromethane in the absence. of base, s uch as pyridine. These results supported the addition-elimination mech anism. The processes of the addition and elimination were confirmed by the H-1 NMR spectrum and kinetic study which led to the following res ults: The addition products 7 and 8 were formed through a stepwise tra ns addition, and the trifluoroacetylated olefins 5 and 6 were self-cat alytically formed from the addition products 7 and 8 through Ei, E2, o r E1, depending on the stability of the cationic intermediates 3 and 4 .